A hybrid-electric vehicle (HEV) includes an engine to provide power for propulsion and accessories. The HEV may include one or more electric machines powered by a traction battery to provide power for propulsion and accessories. During operation, the engine may drive the electric machines to charge the traction battery. The traction battery may then be discharged to drive the electric machines or other accessories. One accessory is an air-conditioning (A/C) compressor to provide cabin cooling. The A/C compressor may be driven by an electric machine that draws power from the traction battery. Electrical power for the A/C compressor is supplied by the traction battery or the electric machine driven by the engine. The power flow between the engine and the traction battery includes opportunities for losses. Efficiency of the electric machines, power electronics, and losses in the traction battery affect the amount of energy that is stored.